The present invention relates to methods for controlling combustion processes in engines that utilize late direct cylinder injection of fuel, such as diesel engines, to reduce harmful emissions produced thereby. For ease of reference, this application may at times simplistically refer only to diesel engines, however, the scope of the invention equally applies to other engines that utilize late direct cylinder injection of fuel as well.
Internal combustion engines which utilize late direct cylinder injection of fuel, such as conventional diesel engines, emit harmful pollutants such as nitrogen oxides (NOx) and particulate matter (PM) substantially in excess of acceptable environmental levels. Nevertheless, because of their fuel efficiency, diesel engines remain preferable to gasoline engines for many vehicle applications.
Despite concerted efforts to reduce NOx and PM emissions in diesel engines, the prior art has never been successful in developing a robust diesel combustion system (i.e. providing commercially acceptable responsiveness and power) that is capable of simultaneously maintaining engine-out emission levels of NOx and PM within environmentally acceptable levels across transients. Instead, it is well known that transient changes in the operating conditions of a diesel engine, specifically with regard to adjustment of fuel feed, exhaust gas recirculation (EGR) and turbocharging levels upon vehicle acceleration, can result in significant NOx or PM emissions. Such emissions during transient changes can cause vehicles to fail emission standards even where such vehicles could meet the emission standards at steady state conditions.
It is therefore an object of the present invention to provide an improved method for enabling low emission, controlled temperature combustion, including during transient changes in operating conditions, for engines utilizing late direct cylinder injection of fuel.